The invention is based on a FMCW radar sensor for a vehicle for detecting objects. It is already known to use one common antenna for a FMCW radar sensor for both transmission and reception. The transmission and reception signals are separated with a circulator produced by waveguide technology. Such technologies are quite expensive and can therefore be used only for special cases but not for simple vehicle applications.
European Patent Disclosure EP 498 542 A2 also discloses a bistatic FMCW radar sensor, in which separate transmitting and receiving antennas have been proposed. With this arrangement, it is true that the expensive circulator can be dispensed with. It is disadvantageous, however, that in this sensor separate antennas are necessary for transmission and reception, with two dielectric lenses. As a result, the expense is again increased.
The FMCW radar sensor according to the invention for a vehicle for detecting one or more objects has the advantage over the prior art that on the one hand the same antennas can be used for transmission and reception. On the other, the expensive circulator for separating the transmission and reception signals is not needed, resulting in a simple design for the FMCW radar sensor. It is also especially advantageous that the microstrip form makes the design very inexpensive. Complicated work to adjust the antennas is also eliminated.
Advantageous further features of and improvements to the FMCW radar sensor disclosed in the main claim are possible as a result of the provisions recited in the dependent claims. It is especially favorable that the illumination of the lens in transmission and reception is improved by the dielectric polyrod antenna.
The lens advantageously has an elliptical shape, so that particularly in an optimized antenna array, the lens is fully illuminated. As a result, the target will not be lost even if the vehicle has a strong tendency to rocking, since the target is always within the radiation range of of the antennas.
By rotating the side-by-side antennas (antenna feeds) by an angle of about 45.degree. relative to the lens axis, a decoupling from objects that must for instance be distinguished from oncoming motor vehicles on a road is accomplished in a simple way. For decoupling the antenna feeds from one another in an embodiment with three antenna feeds, conversely, the middle antenna feed can advantageously be disposed rotated by about 135.degree..
It is also advantageous to switch the Gunn oscillator from the waveguide plane to the microstrip plane via a tapping transformer. Simple coupling of the high-frequency signals is thereby accomplished.
To reduce the mean transmission power, the transmission power can be blanked after the conclusion of the ramp function. The Gunn oscillator is then varied linearly in its frequency only during the ramp times.
It is also advantageous, particularly in a multiramp method, to embody the ramp function as trapezoidal or triangular, so that objects located at various distances can be more easily recognized.
With the aid of the evaluation circuit, not only the vehicle speed, distance and driving angle but also the relative distance from the detected object can be determined.
By incorporating the FMCW radar sensor in a hermetically sealed housing, the vulnerable components are protected against such external factors as dirt and moisture. To compensate for the pressure differences arising from temperature fluctuations, a pressure compensation element is provided, which is advantageously disposed on the outer wall of the housing. As a result, a constant internal pressure is largely achieved, thereby averting dew formation in the housing.
A preferred application of the FMCW radar sensor is to measure distance when the sensor is used in combination with a vehicle speed controller, or as an aid in parking a motor vehicle.